The X'd out 4 can only have 2 more black squares, and the black 6 can only have one more white square, so the white 5 below-to-the-right of the 4 can be X'd out, and the empty square below-to-the-left of the 6 must be black. You can then complete the squares around the black 5 to-the-right of the 4 and then easily finish the rest.